Recently, an ad hoc network system has been proposed in which a plurality of wireless terminals mutually connect by themselves. In the ad hoc network system, no access point is set, and each wireless terminal relays a packet received from a wireless terminal mutually connected thereto to an adjacent wireless terminal based on routing information, so as to form a route according to an environment. For example, sensor data measured at each wireless terminal is relayed to one or a plurality of wireless terminals based on the generated route, and sent to a target wireless terminal, as proposed in Japanese Laid-Open Patent Publication No. 2012-199703 and No. 2009-267532, for example.
In the ad hoc network system described above, there are cases in which a failure such as a facility stop occurs due to a failure of the wireless terminal, insufficient power from a battery, or the like. When the failure of the wireless terminal occurs, the relaying wireless terminal cannot send or receive data, and the sensor data is not sent to the target wireless terminal in a case in which there is no substitute route to bypass the failed wireless terminal. With respect to the failed wireless terminal, a manual operation or maintenance is required to repair the failed wireless terminal, replace the battery or a component of the failed wireless terminal, or the like. However, in a case in which only limited personnel can cope with the the failure of the wireless terminal, it is difficult to immediately cope with the failure of the wireless terminal, particularly when the failure is generated in a large number of wireless terminals.
For example, minor failures may be generated in the wireless terminal. In this case, instead of immediately coping with each minor failure, an efficiency of coping with the minor failures can be improved by collectively coping with the minor failures after the minor failures are accumulated to a certain extent. On the other hand, it is desirable to immediately cope with a major failure generated in the wireless terminal. The major failure may be a loss of a large amount of sensor data, a network facility stop, or the like, for example.
In the case of the ad hoc network system, depending on the route that includes the wireless terminal in which the failure is generated, the relaying wireless terminal can be substituted by dynamically changing to a route that relays via another wireless terminal. However, depending on the location of the wireless terminal in which the failure is generated, there are cases in which the substitute route does not exist.
For this reason, it is desirable to set a priority of coping with the failure, based on an importance of the wireless terminal in which the failure is generated. The importance of the wireless terminal may be computed based on a number of substitute routes, a number of routes passing the target wireless terminal, or the like, for example.
However, the number of substitute routes is computed by aggregating adjacent tables of all of the wireless terminals within the ad hoc network system to a predetermined wireless terminal, for example, and computing the number of substitute routes based on routing information that is constructed from the adjacent tables of each of the wireless terminals. The adjacent table of one wireless terminal includes information of the wireless terminals that are adjacent to this one wireless terminal. Hence, an amount of communication required to collect the adjacent tables becomes considerably large, to thereby put a load on the ad hoc network system. In addition, a storage of the wireless terminal requires a storage capacity that is sufficiently large to store the adjacent tables. Furthermore, because the predetermined wireless terminal to which the adjacent tables are aggregated computes the substitute route by repeating a process similar to the construction of the routing information based on the adjacent tables, a large load is easily applied to the predetermined wireless terminal, and the process of the predetermined wireless terminal requires a long time to perform.
According to the related art, it takes time to perform the process of computing the importance of the effects of the mobile terminal in which the failure is generated on the entire ad hoc network system, and the wireless terminal may easily assume a high-load state. For this reason, it takes time to judge, based on the importance, whether a prioritized maintenance is to be performed with respect to the wireless terminal in which the failure is generated.
Other related art includes Japanese Laid-Open Patent Publications No. 2003-203021 and No. 2003-177945, for example.